Tacky floor pad

ABSTRACT

A throw-away pad, especially for use at the entrance to a clean area but not exclusively for such use. Of multiple ply construction, it comprises a plurality of very thin poly-ethylene or polypropylene sheets, of suitable surface size and shape to receive at least a pair of shod feet. Each sheet bears a very thin coating of pressure-sensitive adhesive on its top surface. The bottom surface of the pad, that is, the bottom of the lowermost sheet thereof, also is coated with adhesive so that the pad, when in use, is removably adhered to the floor. The pressure-sensitive adhesive has a low modulus of elasticity, a high internal viscosity and high surface free energy, so that it firmly and aggressively grabs dirt from shoes of wheels passing over it, yet each sheet can be readily peeled off after use to expose a fresh adhesive surface to further traffic. The entire pad or stack is thin to present no hazard or obstacle to foot or to wheeled vehicles, e.g., to a gurney being wheeled into an operating room.

14 1 Jan. 15, 1974 1 1 TAClKY FLOOR PAD Homer C. Amos, Palm Springs,Calif.

[73] Assignee: Edward T. Strickland, Palm Springs,

Calif. a part interest [22] Filed: Nov. 1, 1971 [21] Appl. No: 194,623

[75] Inventor:

CLEAN RODIVI Primary Examiner-Alfred C. Perham Attorney-Robert E.Wickcrsham ABSTRACT A throw-away pad, especially for use at the entranceto a clean area but not exclusively for such use. Of multiple plyconstruction, it comprises a plurality of very thin poly-ethylene orpolypropylene sheets, of suitable surface size and shape to receive atleast a pair of shod feet. Each sheet bears a very thin coating ofpressure-sensitive adhesive on its top surface. The bottom surface ofthe pad, that is, the bottom of the lowermost sheet thereof, also iscoated with adhesive so that the pad, when in use, is removably adheredto the floor. The pressure-sensitive adhesive has a low modulus ofelasticity, a high internal viscosity and high surface free energy, sothat it firmly and aggressively grabs dirt from shoes of wheels passingover it, yet each sheet can be readily peeled off after use to expose afresh adhesive surface to further traffic. The entire pad or stack isthin to present no hazard or obstacle to foot or to wheeled vehicles,e.g., to a gurney being wheeled into an operating room.

23 Claims, 5 Drawing Figures PATENTEBJAH 15 m4 SHEET 10? 2 CLEAN ROCJMFIG. I 12 WNVENTOR HOMER c. AMOS BY M 5 I r. 5 I

ATTORNEYS Pmmwmwmq BJVBEJOE SHZET 2 CF 2 INVENTOR HOMER c AMOS TACKYFLOOR PAD BACKGROUND OF THE INVENTION This invention relates to athrow-away pad of tackyor sticky-surfaced sheets for removing dust anddirt from shoe soles, wheels and the like passing thereover, to assistin maintaining a clean area such as a hospital room or surgery in thedesired clean condition. The pad or stack of sheets is adhered removablyto a floor in suitable relationship to the room to be protected, andeach sheet can be separately removed as used to present a fresh tackysurface for use.

With the rise of modern technology, clean rooms have become increasinglyimportant. In the surgery, scrupulous cleanliness is vitally importantto prevent infection. The indiscriminate use of antibiotics has causedthe emergence of strains of resistant bacteria, and the unpleasantresult has been that hospitals, instead of being sanctuaries ofsterility, have become a source of new infections that are extremelydifficult to combat. More scrupulous cleanliness is a better answer tothe problem than is the continual indiscriminate use of antibiotics.

Similarly, in areas where microcircuitry and delicate space-ageinstruments are manufactured, one speck of dust can cause failure.Hence, techniques insuring the highest possible degree of cleanlinesshave received intensive study.

Two fruitful sources of dirt are shoe soles and cart wheels. Manyefforts have been made to find an easy and convenient but yet effectivemethod for removing dust and dirt from shoes, and in the case ofsurgeries, from the wheels of the cart on which the patient is movedabout. Heretofore, such removal has been of varying degrees of efficacyor lack of it and of inconvenience. For example, air blast systems havenot been very effective, and disinfectant wash troughs have been messyand have been impractical for cart wheels.

Various types of sticky pads have been tried heretofore, but haveexhibited certain disadvantages. In our co-pending patent application,Ser. No. 47,453 filed June 18, 1970 now U.S. Pat. No. 3,717,897, thereis described the construction of an inexpensive washable pad which canbe made by anyone skilled in the art of coating adhesives. The cost ofthe pad originally is quite low, and it can be washed with water, orsoapy water, to remove adhering dirt, so that its use is inexpensive.Furthermore, it can be washed repeatedly without substantially losingits effectiveness, so that the cost per fresh sticky surface isextremely low. However, as hourly wages climb ever higher and highermuch effort is being expended to cut man-hours to an absolute minimum.resulting in a marked trend to one-use throw-aways, even in such itemsas hypodermic syringes. The pad of the present invention avoids thelabor attendant upon renewing the fresh sticky surface by washing andprovides such surface merely by peeling off the used sheet to exposesuch desired surface for contained use of the overall pad, and makessuch a method economically feasibly by reason of its extremely low-costconstruction.

SUMMARY OF THE INVENTION The pad of this invention employs apolyethylene or polypropylene sheet which can be walked on and wheeledover without tearing or destruction. A pressure-sensitive adhesiveadvantageously has been found to remove dirt from shoes and wheels whileat the same time it readily releases the polyethylene or polypropylenesheet which covers it to enable presentation of a fresh adhesive surfacefor use. The polyethylene or polypropylene is of such strength that verythin sheets can be used, and a very thin coating of the adhesivedescribed can be employed, thus providing an overall pad which issufficiently thin, even with a relatively large number of sheets, thatthere is substantially no obstruction to walking or to wheeling a cartover the surface of the starting pad, and, of cours, even less as useand removal of sheets proceeds. The adhesive is not unpleasant to walkupon, and, on the other hand, the last sheet can be stripped from thefloor without delamination or tearing when it is completely used or whenthe pad is to be removed for any reason.

The sheets are assembled with the intervening and exterior coatings ofadhesive in a manner to provide a pad having the above advantages andother advantages that will become apparent from the description herein.When a dust-trap floor pad is designed to have a highly aggressive tackto catch and hold dirt well, and is also designed to have sufficientlylow adhesion to the surface beneath in order to make it easy to removewhen it has completed its service life, then a new problem arises. If aclean wheel or shoe is pressed upon it, then the possibility appears ofpulling the whole sheet loose, the sheet possibly ending up wrappedaround the shoe or wheel.

We have found that in the middle of the sheet the vacuum under the sheetprevents this catastrophic failure, and that such failures are initiatedby a peel at the edges. Protection of the edge, therefore, prevents suchfailure, and we have found that if the adhesive on the under side ofasheet extends outwardly slightly further than the adhesive on the topside thereof, a peel will not be initiated. This differential can be assmall as onesixteenth inch and still be remarkably effective, and it canbe as large as about one-fourth inch. One method of achieving thisdifferential is the beveling of the completed pad, which serves tocompress the pad to the floor, thereby preventing up-pull. A /8 to /ainch bevel on a IO-level pad has been found to be an inexpensive buteffective method of preventing lift-up or undesired removal of a sheet.The beveled edge may be dusted with a non-adhesive powder to preventadhesion in this area. In a beveled stack-pad some provision is made tofacilitate the removal of a layer when it has completed its useful life,for example, providing predetermined adhesive-free areas at an edge orcorner portion of each sheet to enable grasping and pulling off of thesheet from the pad.

While any very aggressive pressure-sensitive adhesive mass based onnatural or synthetic rubber may be used herein, the pressure-sensitiveadhesive preferred for use herein is an acrylic latex, acrylic becauseof the very stable properties and long shelf life of acrylics, and latexbecause of the economy, safety, and convenience of lat'ices as comparedwith solutions. Such latex of the proper physical properties has beenfound to adhere sufficiently firmly to the untreated surface of thepolyethylene or polypropylene substrate so that the pad produced isstable in form for handling or shipping, but the latex releases thepolyethylene or polypropylene readily when it is desired to tear away aused sheet. Acrylics, in sharp contrast to most adhesive masses, providean almost indefinitely long shelf life to the product with nodeterioration or shift in properties, and the product exhibits relativeinsensitivity to heat and cold. No solvent is required to apply thelatex, thus lowering the costs in manufacturing the pad, and the latexexhibits no flammability, while air pollution is avoided by its usewithout added solvent. Furthermore, this adhesive is effective in anextremely thin coating layer. The acrylic adhesive used herein issubstantially nonreactive, i.e., of negligible further polymerization,and is of comparatively low molecular weight, for a latex, to obtain avery high surface free energy, i.e., soluble or nearly so in organicsolvents such as tetrahydrofuran. A suitable acrylic latex, for example,is an emulsion polymer prepared from lower alkyl acrylates as the mainmonomers, having a pH of 6 to 6.5, viscosity of between 100 and 300 at aspindle/speed of 2/60, of 57 percent solids, and having a calculatedglass transition temperature of 46 C. Production of such a polymer isdescribed in Belgian Pat. No. 749,689.

In acrylics, the modulus of elasticity can be quite accurately definedin a roundabout way in terms of the glass temperature, i.e., thetemperature at which the torsional modulus is 300 kg/cm The acryliclatex used herein should have a glass temperature of about 45 C., or inthe range of from about 30 C. to about 55 C., so that it is very soft toenhance adhesion but is not too soft for durability. It has a highinternal viscosity which is suitably measured by a method hereinafterdescribed, to give for the present adhesive a tack angle of from 20 to30 against a clean polyethylene surface, and an internal viscosity ofseveral hours, advantageously from to 24 hours.

Internal viscosity in a solid may be a new concept to some people, andan example may help: a vinyl garden hose has a high internal viscosity,while gum rubber has a low internal viscosity. Even though it may beharder, a gum rubber tube suffers no harm from being run over by a car,while a vinyl garden hose (especially if old and cold) can be cracked topieces by the same treatment, because it cannot deform quickly enough,due to its higher internal viscosity. If the rubber tube be heavy andfirm, it may require more weight to flatten it than to flatten the vinylhose; moreover, the rubber flattens partway immediately and stays there,while the vinyl slowly flattens out completely. Hence, the vinyl isconsidered softer because it flattens out further, but it is slow to doso, because it has a higher internal viscosity.

BRIEF DESCRIPTION OF THE DRAWINGS The invention and some modes ofcarrying it out will be illustrated by the following more specificdescription and by the annexed drawings, wherein:

FIG. 1 is a schematic view of the placement ofa pad according to thisinvention in a corridor of a building and just outside the door orentrance to a clean room;

FIG. 2 is an enlarged view in side elevation of a pad according to thisinvention, showing beveled edges and adhesive-free corner surfaces atone end of the sheets to facilitate removal ofa single sheet for renewalof surface; the view is broken in the middle in order to conserve space;

FIG. 3 is a partial top enlarged view of the stack or pad of FIG. 2,illustrating one means of forming the adhesive-free corner surfaces;

FIG. 4 is a partial side view of the article of FIG. 3 after cornertreatment and showing a few sheets of the pad or stack, placement of theadhesive thereon, and the freed corner edges; and

FIG. 5 is a view in perspective of a test-apparatus comprising apolished steel cylinder with scribed lines, with adhesive-coated stripon test and shown in alternative positions.

DETAILED DESCRIPTION OF THE INVENTION As shown in FIGS. 2, 3 and 4, thepad 15 comprises a plurality of sheets 16, suitably five to fifty, ofsuch sheets 16, each being coated with a layer 17 of acrylic latexadhesive as described herein. Each sheet 16 is very thin, being from0.002 to 0.003 inch in thickness, and is of standard grade polyethyleneor polypropylene, in either case with heavy corona discharge adhesiontreatment on one surface which is readily available in commerce at noadditional cost. When the treated surface is coated with the adhesive,good adhesion is obtained between the polyethylene or polypropylene andthe coating. Further, by this means the required differential inadhesion between upper and lower surface is achieved, so that as a usedsheet is stripped off, the adhesive mass always comes away clean fromthe lower surface of the used sheet, and never delaminates away from theupper surface of the new sheet beneath. The layer 17 of thepressure-sensitive adhesive is extremely thin, being from 0.00003 to0.0003 inch, advantageously 0.0001 inch in thickness. Thus, the pad 15containing ten such coated sheets is less than one thirty-second inch inthickness and does not present an obstacle to foot traffic or causejarring or shock to a patient on a gurney when wheeled over such pad 15.

The bottom sheet, or all of them, may be of colored polyethylene orpolypropylene, or the whole set may be transparent, or they or some ofthem may be imprinted with a decorative design, as desired.

Since the bottom sheet must be of sufficient strength to withstandremoval without tearing from a floor whose adhesion may be greater thanuntreated polyethylene or polypropylene, a heavier film such as 0.004inch is preferred.

Each sheet 16 is of polyethylene or polypropylene of the thicknessdescribed, and it is coated with a layer 17 of the acrylic adhesive overthe entire upper surface of each sheet 16, except that a corner area orportion 18 is free of adhesive so that the sheet 16 can be easilygrasped and stripped off after use. This is shown in exaggerated form inFIG. 4, and will be further described below. The lowermost sheet 16 hason its undersurface 22 a layer 23 of adhesive to removably affix the pad15 to floor 14. The adhesive 23 may cover all of the underside of thelowest layer or a portion only, such as the edge portions. As shown inFIG. 1, the pad 15 or several such pads are arranged to be large enoughto cover the floor areajust outside of the entryway 11 so that allpersons or the full perimeter of the wheels of vehicles entering theclean room 14 must pass thereover, and the adhesive layer 17 removesdust and dirt from wheels and shoes as they come into contact with suchlayer 17. After use, and as determined by the appearance of the topsheet, it is stripped off and a fresh surface exposed, down to the lastsheet 16 of the stack 15.

We have found that the same coating may be used as the adhesive 23 whichholds the pad 15 to the floor. However, since there is little controlover the type of surface to which the pad 15 may be called upon toadhere, it has been found preferable to have this particular adhesivecoating 23 thicker, such as a thickness of 0.0015 inch.

Internal viscosity is inconvenient to measure in terms of poises, andsurface free energy is so difficult to measure in terms of ergs persquare centimeter as to be impractical. Therefore, we have devised asimple empirical test to evaluate adhesives for possible use in thepresent invention.

FIG. 5 shows a polished steel cylinder 25, two inches in diameter,scribed with fine lines 26 parallel to the axis 27 and 5 apart over 90of its surface 28. The cylinder 25 is mounted firmly in cantilever withthe axis horizontal, in the position shown in FIG. 5. The cylinder 25 iscovered with a cemented-on film of clear untreated polyethylene orpolypropylene. A one mil film of the adhesive 29 under test is cast on apolyethylene terephthalte (Mylar) strip 30 of one mil thickness, whichis then trimmed to a width of one inch. The polyethylene orpolypropylene surface of the cylinder 25 is washed carefully with methylethyl ketone, and the strip 30 is placed over the scribed lines 26 andone end 31 draped over the top. The strip 30 is pressed firmly againstthe cylinder 25 to attain as near as possible 100 percent contact area.A l-gram weight 32 is hung gently on the trailing end 33 and the timenoted at the 90 position. The progress of the peel line is noted fromtime to time and it should come to a point within of its final positionin the times noted below. The total time allowed must be ample toascertain that the peel line has in fact stopped moving, to insure thatinternal viscosity is not affecting the result. If the line is stillmoving after 30 hours, the formulation may be discarded as having toohigh an internal viscosity for a shoe-cleaning pad.

From this test, two things can be learned:

1. The stopping position of the peel line is a measure of the permanenttack of the adhesive in question against clean untreated polyethylene orpolypropylene. Much experience has shown that the optimum for bestall-around performance of the coatings l7 and 22 is given by an adhesivethat stops at approximately 35. Values in the range of about to about 50will give reasonable success, and very good results are obtained in arange of about 25 to about 40.

2. The length of time from start to within 5 of finish (the finish issurprisingly definite though the high cold flow contributes a very slowmovement of about 3 or 4 per day after the true peel motion has ceased)is a measure of the internal viscosity. The time should be in the rangeof 600 to 1,800 minutes, preferably from 900 to 1,500 minutes, andoptimum results are generally obtained at about 1,200 minutes.

In a typical example according to this invention, a series of sheets ofstandard grade polyethylene having heavy corona discharge treatment onthe upper surface thereon are cut to the desired size to make a padsuitable for placement before an entryway to a surgical operating roomin a hospital. The polyethylene sheet material is from 0.002 to 0.003inch in thickness. If thinner than 0.002 inch, the sheet may teareasily, and if it is thicker than 0.003 inch it is unnecessarily thickand expensive. The sheets 16 are of such size to be wide enough to spanthe entryway for which the pad 15 is intended and longer than a largestep taken by a walking person, and will also receive the full perimeterof the wheel of such wheeled cart as may be encountered, for example, ahospital gurney. The size of the sheets may be such that they may beused in modular fashion, and two or three or more may be placed side byside to cover wide areas. A mixture is prepared of an acrylic latex, oroflatices, to arrive at the properties described above, and of asurfactant such as sodium salt of a sulfonated alkyl ester, available incommerce under the trademark Triton Gr 5, sufficient, suitably about0.22 percent by weight of the total mixture, to effect good wetting whenthe mixture is coated onto the polyethylene. If desired, bacteriostatsor anti-static components or both may be added. After these componentsare thoroughly admixed to form the desired adhesive, it is coated ontoeach sheet to cover the treated surface. The surface of each sheet asdescribed is completely covered, and the sheets are stacked upon eachother in the order of sheet of polyethylene adhesive layer sheet ofpolyethylene, etc. until from five to 50 of such sheets have beenassembled into a stack. The bottom sheet is covered with the adhesive onits underside to cause it to adhere in place to the floor, and theassembled stack is beveled on all four sides, suitably about to /8 inchfor a 10-sheet stack. The procedure with polypropylene sheets is thesame.

A pad of thick felt or polyurethane foam, or like absorbent material 35is placed diagonally across a corner of pad 15. By any desired method,such as spraying, for example, the pad is wetted with a small amount ofa suitable solvent for the adhesive, such as toluene, and the wholeallowed to stand for several minutes, after which the pad is removed. Itis then found that each sheet 16 up the stepped bevel has lifted alongthe corner portion 18 to a width of about one-fourth inch. Excesssolvent is then blown off and talc or other suitable dry powdered,preferably mineral, solid is brushed under the lifted edges, the powderdestroying the effectiveness of any adhesive which it covers.

When the pad is in place on a floor etc., as each sheet is exhausted ofits dirt-grabbing property, it can be grasped by the hand or otherwiseat the lifted corner to be pulled off to expose a fresh, clean adhesivesurface.

The stack or pad is now ready for use and is placed before an entrywayto a surgical operating room or industrial clean-room on the floor ofthe corridor leading thereto. After foot traffic and normal wheeledtraffic have passed over the top sheet for from several hours to severaldays, depending on the traffic, and the adhesive has grabbed the pulleddirt and lint therefrom, the sheet is grasped by its adhesive-free edgeand stripped from the stack, exposing the next adhesive surface for use.

The pad is also useful at the doors of clean rooms in hospitals or inhomes or wherever dust control and cleanliness are desired.

It will be understood that the above specific description and thedrawings have been given for purposes of illustration only and thatvariations and moficiations can be made therein without departing fromthe spirit and scope of the appended claims.

Having now described the invention, what is claimed 1. A thin,throw-away cleansing pad adhesively and removably securable to a floorand adapted to form a substantially unobstructing portion of a pathwayfor foot or wheeled-cart traffic, comprising:

a. a plurality of sheets formed from a material selected from the groupconsisting of polyethylene is about 0.0001 inch in thickness.

about 0.4 percent of said surfactant and about 99.60 percent of saidacrylic resin.

inwardly by virture of each sheet being larger in both lengthwise andwidthwise dimensions than the sheet above it, the area of a lower sheetwhich projects beyond the sheet above being non-adhesive.

and polypropylene, in detachably stacked arrangement,

b. each said sheet having an upper surface and a lower surface, theupper surface only having been coronadischarge-treated to improveadhesion thereto to an adhesive and rendering said upper surfacepreferentially adherent to said adhesive relative to said untreatedlower surface, and

c. a thin pressure-sensitive adhesive coating substantially covering andadhered to said upper surface of 10 each said sheet and constituting theonly material in between successive said sheets,

d. said adhesive coating on said sheet extending further outwardly thansuch coating on the next higher sheet in said pad, to prevent peel andunwanted delamination from normal use.

2. The pad of claim 1 wherein said adhesive is an 3. A pad as in claim 1wherein each said sheet is from 0.002 to 0.004 inch in thickness andsaid adhesive coating is about 0.00003 to 0.0003 inch in thickness.

4. A pad as in claim 3 wherein said adhesive coating 5. A pad as inclaim 1 wherein said adhesive is an intimate admixture of an acrylicresin and a surfactant in amount sufficient to effect wetting when saidadmixture is coated onto a polyethylene substrate, exhibits a Youngsmodulus of-45 C. expressed as glass temperature; and has a tack angle ofabout 20 to and an internal viscosity of from 5 to 24 hours as measuredby the tests described herein by covering the steel cylinder describedin said tests with a clean polyethylene surface, coating a polyethyleneterephthalate strip with a layer of said adhesive mixture 0.001 inchthick, applying said coated strip over said polyethylene surface with100 percent surface contact, hanging a 100 gram weight on a trailingedge of said strip to peel said strip from said surface to anequilibrium point, coming to a point within 5 of said equilibrium pointwithin from 10 to 30 hours.

6. A pad as in claim 5 wherein said adhesive contains 7. A pad as inclaim 1 wherein each said sheet has a corner area free of adhesive toenable grasping and removal of said sheet.

8. A pad as in claim 1 having beveled edges tapered 9. A pad as in claim1 wherein each said adhesive coating extends outwardly at leastone-sixteenth inch farther than the next higher coating.

10. A pad as in claim 1 wherein the lowermost sheet is coated with thesame adhesive on its bottom surface in a thicker coating.

. 11. A clean room entryway lncludmg In combination:

wheel, and longer than a large step taken by a person walking, wherebyto remove dust and dirt from wheels and shoes coming into contacttherewith,

d. said pad assembly comprising at least one stack of a plurality ofsheets formed from a material selected from the group consisting ofpolyethylene and polypropylene, in detachably stacked arrangement, theupper surface only of each said sheet being corona-discharge treated togrealy improve adhesion, each said sheet having a thin layer ofpressure-sensitive adhesive, substantially covering and adhered to saidupper surface thereof and constituting the only material in betweensheets, each downwardly succeeding layer of said adhesive extendingoutwardly farther than the next adjacent upper layer thereof to preventpeel and unwanted lamination being brought about by normal use.

12. A clean room entryway as in claim 11 wherein each said sheet is from0.0002 to 0.004 inch in thickness and each said adhesive layer is about0.000] inch in thickness.

13. A clean room entryway as in claim 11 wherein said adhesive is anacrylic latex adhesive, has a Youngs modulus of from about 30 C. toabout 50 C. expressed as glass temperature, a tack angle of from 20 to30 and an internal viscosity of from 10 to 30 hours when measured bytests described in this specification.

14. A clean room entryway as in claim 11 wherein said pad is adhered tosaid floor by the same adhesive material in a thicker layer.

15. A clean room entryway as in claim 11 wherein each said sheet has acorner portion freed of adhesive to enable grasping and lifting.

16. A clean room entryway as in claim 15 wherein each said succeedinglayer of said adhesive extends at least 1/16 inch outwardly from saidadjacent upper layer.

17 A clean room comprising walls, floor and ceiling defining a room, adoorway in one said wall, a hallway floor outside said doorway, and anunframed cleaning pad having beveled edges and adhesively and removablysecured directly to said floor outside of said doorway and adapted toreceive on its upper surface foot traffic and wheeled traffic, said padbeing larger than a long step taken by a walking person and adapted toreceive the full perimeter of the wheel of a wheeled cart, whereby toremove dust and dirt from wheels and shoes coming into contacttherewith, said pad comprising a plurality of thin sheets formed from amaterial selected from the group consisting of polyethylene andpolypropylene, in detachably stacked arrangement, each said sheet havinga layer of pressure-sensitive adhesive substantially covering the upperface thereof, said upper face only having been corona-dischargepretreated to improve adhesion to an adhesive, each said sheet exceptthe bottom being from 0.002 to 0.003 inch in thickness and said adhesivelayer being from 0.00003 to 0.0003 inch in thickness, said pad having athicker bottom sheet with a bottom surface and a thicker layer ofadhesive disposed thereover to adhere said pad to said floor, eachdownwardly succeeding layer of said adhesive extending outwardly fartherthan the next adjacent upper layer of said adhesive in order to preventundesired peeling upon normal use.

18. A clean room as in claim 17 wherein said firstmentioned adhesivelayer is 0.001 inch in thickness.

19. A clean room as in claim 17 wherein said first mentioned adhesivehas a Youngs modulus of from -30C. to 55C. expressed as glasstemperature a tack angle of from 20 to 30 and an internal viscosity offrom to 30 hours when measured by tests described in this specification.

20. A clean room as in claim 19 wherein the secondmentioned adhesive isthe same as the first-mentioned adhesive.

21. A clean room as in claim 17 wherein each sheet has a corner portionfreed of adhesive to enable grasping and lifting.

22. A clean room as in claim 17 wherein each said succeeding layer ofsaid adhesive extends at least onesixteenth inch outwardly from saidadjacent upper layer.

23. A thin, throw-away cleansing pad adhesively and removably securableto a floor and adapted to form a substantially unobstructing portion ofa pathway for foot or wheeled-cart traffic, comprising:

a. a plurality of sheets formed from a material selected from the groupconsisting of polyethylene and polypropylene in detachably stackedarrangement, each said sheet having an upper surface and a lowersurface, and

b. a thin pressure-sensitive adhesive coating substantially covering andadhered to said upper surface of each said sheet and constituting theonly material in between successive said sheets,

c. said adhesive coating on each sheet extending further outwardly thansuch coating on the next higher sheet in said pad, to prevent peel andunwanted delamination from normal use.

MCCOY M. GIBSON, JR. C. MARSHALL DANN UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Potent No. 3,785,102 Dated January 15, 1974Inventor(s) Homer C. Amos It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 1, line 59, "contained should read --continued,

Column 1, line 60, "feasibly" should read --feasible--.

Column line 11, "cours" should read --course--.

Column Column 6, line 57, "moficiations" should read --modifications--.

7, line 13, "on said sheet" should read --on each sheet-- Column line 9,.grealy" should read --greatly--.

Signed and sealed this 6th day of August 1974.

(SEAL) Attest:

Attesting Officer Commissioner of Patents

2. The pad of claim 1 wherein said adhesive is an acrylic latex having atack angle of from 20* to 30* and an internal viscosity of severalhours, as determined by the tests described in this specification.
 3. Apad as in claim 1 wherein each said sheet is from 0.002 to 0.004 inch inthickness and said adhesive coating is about 0.00003 to 0.0003 inch inthickness.
 4. A pad as in claim 3 wherein said adhesive coating is about0.0001 inch in thickness.
 5. A pad as in claim 1 wherein said adhesiveis an intimate admixture of an acrylic resin and a surfactant in amountsufficient to effect wetting when said admixture is coated onto apolyethylene substrate, exhibits a Young''s modulus of -45* C. expressedas glass temperature; and has a tack angle of about 20* to 30* and aninternal viscosity of from 5 to 24 hours as measured by the testsdescribed herein by covering the steel cylinder described in said testswith a clean polyethylene surface, coating a polyethylene terephthalatestrip with a layer of said adhesive mixture 0.001 inch thick, applyingsaid coated strip over said polyethylene surface with 100 percentsurface contact, hanging a 100 gram weight on a trailing edge of saidstrip to peel said strip from said surface to an equilibrium point,coming to a point within 5* of said equilibrium point within from 10 to30 hours.
 6. A pad as in claim 5 wherein said adhesive contains about0.4 percent of said surfactant and about 99.60 percent of said acrylicresin.
 7. A pad as in claim 1 wherein each said sheet has a corner areafree of adhesive to enable grasping and removal of said sheet.
 8. A padas in claim 1 having beveled edges tapered inwardly by virture of eachsheet being larger in both lengthwise and widthwise dimensions than thesheet above it, the area of a lower sheet which projects beyond thesheet above being non-adhesive.
 9. A pad as in claim 1 wherein each saidadhesive coating extends outwardly at least one-sixteenth inch fartherthan the next higher coating.
 10. A pad as in claim 1 wherein thelowermost sheet is coated with the same adhesive on its bottom surfacein a thicker coating.
 11. A clean room entryway including incombination: a. an entrance doorway leading into said clean room, b. acorridor leading to said doorway and having a floor, and c. an unframedpad assembly having beveled edges, for cleaning shoes and wheelsdisposed adhesively directly to said floor just outside said doorway andlarge enough to receive the full perimeter of such wheel, and longerthan a large step taken by a person walking, whereby to remove dust anddirt from wheels and shoes coming into contact therewith, d. said padassembly comprising at least one stack of a plurality of sheets formedfrom a material selected from the group consisting of polyethylene andpolypropylene, in detachably stacked arrangement, the upper surface onlyof each said sheet being corona-discharge treated to greatly improveadhesion, each said sheet having a thin layer of pressure-sensitiveadhesive, substantially covering and adhered to said upper surfacethereof and constituting the only material in between sheets, eachdownwardly succeeding layer of said adhesive extending outwardly fartherthan the next adjacent upper layer thereof to prevent peel and unwantedlamination being brought about by normal use.
 12. A clean room entrywayas in claim 11 wherein each said sheet is from 0.0002 to 0.004 inch inthickness and each said adhesive layer is about 0.0001 inch inthickness.
 13. A clean room entryway as in claim 11 wherein saidadhesive is an acrylic latex adhesive, has a Young''s modulus of fromabout -30* C. to about -50* C. expressed as glass temperature, a tackangle of from 20* to 30* and an internal viscosity of from 10 to 30hours when measured by tests described in this specification.
 14. Aclean room entryway as in claim 11 wherein said pad is adhered to saidfloor by the same adhesive material in a thicker layer.
 15. A clean roomentryway as in claim 11 wherein each said sheet has a corner portionfreed of adhesive to enable grasping and lifting.
 16. A clean roomentryway as in claim 15 wherein each said succeeding layEr of saidadhesive extends at least 1/16 inch outwardly from said adjacent upperlayer. 17 A clean room comprising walls, floor and ceiling defining aroom, a doorway in one said wall, a hallway floor outside said doorway,and an unframed cleaning pad having beveled edges and adhesively andremovably secured directly to said floor outside of said doorway andadapted to receive on its upper surface foot traffic and wheeledtraffic, said pad being larger than a long step taken by a walkingperson and adapted to receive the full perimeter of the wheel of awheeled cart, whereby to remove dust and dirt from wheels and shoescoming into contact therewith, said pad comprising a plurality of thinsheets formed from a material selected from the group consisting ofpolyethylene and polypropylene, in detachably stacked arrangement, eachsaid sheet having a layer of pressure-sensitive adhesive substantiallycovering the upper face thereof, said upper face only having beencorona-discharge pretreated to improve adhesion to an adhesive, eachsaid sheet except the bottom being from 0.002 to 0.003 inch in thicknessand said adhesive layer being from 0.00003 to 0.0003 inch in thickness,said pad having a thicker bottom sheet with a bottom surface and athicker layer of adhesive disposed thereover to adhere said pad to saidfloor, each downwardly succeeding layer of said adhesive extendingoutwardly farther than the next adjacent upper layer of said adhesive inorder to prevent undesired peeling upon normal use.
 18. A clean room asin claim 17 wherein said first-mentioned adhesive layer is 0.001 inch inthickness.
 19. A clean room as in claim 17 wherein said first mentionedadhesive has a Young''s modulus of from -30*C. to -55*C. expressed asglass temperature, a tack angle of from 20* to 30* and an internalviscosity of from 10 to 30 hours when measured by tests described inthis specification.
 20. A clean room as in claim 19 wherein thesecond-mentioned adhesive is the same as the first-mentioned adhesive.21. A clean room as in claim 17 wherein each sheet has a corner portionfreed of adhesive to enable grasping and lifting.
 22. A clean room as inclaim 17 wherein each said succeeding layer of said adhesive extends atleast one-sixteenth inch outwardly from said adjacent upper layer.
 23. Athin, throw-away cleansing pad adhesively and removably securable to afloor and adapted to form a substantially unobstructing portion of apathway for foot or wheeled-cart traffic, comprising: a. a plurality ofsheets formed from a material selected from the group consisting ofpolyethylene and polypropylene in detachably stacked arrangement, eachsaid sheet having an upper surface and a lower surface, and b. a thinpressure-sensitive adhesive coating substantially covering and adheredto said upper surface of each said sheet and constituting the onlymaterial in between successive said sheets, c. said adhesive coating oneach sheet extending further outwardly than such coating on the nexthigher sheet in said pad, to prevent peel and unwanted delamination fromnormal use.